This invention concerns specialized circuits which are used to form an interface between a chip card, also known as a "microprocessor card" or chip card and the operating circuits in the reader to which the card is connected in order to operate it.
Microprocessor cards currently known can contain highly diverse printed circuits, ranging from a simple memory chip (telephone card) to a complete microprocessor with RAM and ROM. However, their physical interface is standardized in terms of the number (normally 8) and assignment of contacts with the outside world, namely with the different readers which are used, first of all to programme the card during the manufacturing process and then to operate it when in service. Certain voltages, such as programming voltages, for example, may differ from one card to another.
Furthermore, the software interface (or protocol), in other words the sequencing of signals on the contacts, is either standardized, in the case of asynchronous circuits (ISO norm) or non-standardized, in the case of synchronous circuits.
For example, for a synchronous circuit (generally a memory chip alone, without a microprocessor), one has direct current circuit power connections, earth connections, trigger connections (RST) and three connections which transmit clock signals (CLK), data signals (I/O) and signals for conditioning the memory into read or write (R/W). It is also possible, for example, with this type of synchronous circuit, for the clock pulse count to address successive memory cells in this memory. Non-standardized management protocols in these synchronous circuits use, in particular, all four of the above connections (RST, CLK, I/O, R/W) in order to operate the card.
The circuits in the reader form a computer system based on one or more microprocessors and are comparable to a common-type micro-computer. To form the interface between this computer system and the chip card, specialized integrated circuits, providing the following functions, are generally used:
management of voltage sequencing during powering of the chip card;
protection against overvoltage or short-circuits,
management of voltage sequencing when the card is removed from the reader,
generation of regulated supply and programming voltages (VCC and VPP),
management of 8 card contacts,
software interfacing.
In particular, we can quote the L 6603 and L 6604 circuits made by SGS THOMSON and MTC 6012 A and 6012 from MIETEC. The purpose of specialized circuits is to determine whether the clock connections, data signal transmission connections and read/write conditioning connections are short-circuited, or even to determine whether the current in the card is too high.
There are therefore two types interface: a first interface between these specialized circuits and the chip card, and a second interface between these specialized circuits and the reader's data processing system. In terms of the chip card, the interface is well determined, from a physical point of view, but as there are two types of card (synchronous and asynchronous), it must be a dual type. In terms of the reader's data processing system, the interface varies greatly from one specialized circuit manufacturer to another. However, all specialized circuits include status registers, which report normal operation or any faults detected. These status registers are loaded with one word per test carried out. To obtain information about the operation of a chip card, you must read these status registers.
In the circuits which are known to this date, the interface between the specialized circuit and the data processing system uses a great many connections which enable, first of all, the card to be addressed with the necessary signals and, secondly, the different internal circuit registers, which are used to carry out the functions listed above, to be managed. We therefore often find:
8 connections, generally called D0-D8, corresponding to the data bits to be written in these registers,
a certain number of control connections (usually 3), enabling this data to be read and written in the registers,
a connection for each signal on the printed circuit card which the interface is capable of managing (all are not always available).
In addition to the hardware complexity resulting from this large number of wires (one per connection), this requires an additional software interface in the data processing system in order to manage the relations with the specialized circuit. At the same time, irrespective of the chip to be managed, we already have at least the card/reader software interface (synchronous or asynchronous) which is needed to manage the card or the reader, and very often both, as the software interface with asynchronous circuits is standardized, and therefore well known. It is therefore possible to have this interface without any additional information about the chip.
The purpose of the invention is to reduce the number of connections between the reader's data processing system and the specialized circuit, to reduce, in practice, the number of connection pins in the specialized circuit, and to ensure that the reader's data processing system only needs to know two interfaces instead of three. For this purpose, the interface between the specialized circuit and the data processing system of the reader is such that it emulates completely the interface between this specialized circuit and a synchronous type chip card (same number of connections, same protocol). In this case, we still have three interfaces, one between the data processing system and the specialized circuit and two between this specialized circuit and the chip cards, but the first interface is the same as one of the last two: it corresponds to synchronous chips.